These microorganisms usually enter the body through mouth, nose and eyes, and then infect the lungs, especially the air sacs
or alveoli of the lungs.
Pneumonia is more commonly found to affect the lower lobes of the lungs. Apart from microorganisms, pneumonia can also be caused by any injury or damage to the lungs, caused by the exposure to certain chemicals and radiation. So, many times, people receiving aspiration or radiation therapy can too get pneumonia". This is the link:
http://www.